Question: What is Replication in MongoDB?
Replication is the process of synchronizing data across multiple servers.
Replication increases data availability with multiple copies of data on different database servers.

Question: How replication works in MongoDB?
A replica set is a "group of mongod instances" that host the same data set.
In a replica set one node is primary node and remaining nodes are secondary.
In a replica one node is primary node that receives all write operations.
All data replicates from primary to secondary node.

Question: What is Sharding?
Sharding is the process of storing data records across multiple machines to meeting the demands of data growth.

Question: What is Map-reduce?
Map-reduce is a data processing paradigm for condensing large volumes of data into useful aggregated results.

Question: What is a Covered Query?
It is query in which all the fields in the query are part of an index and all the fields returned in the query are in the same index.